Add tests for the makemigrations override

tests/test_project/makemigrations_backward_incompatible_migration_missing/migrations/0001_initial.py

@@ -0,0 +1,28 @@
+# Generated by Django 2.2 on 2020-06-26 17:49
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = []
+
+    operations = [
+        migrations.CreateModel(
+            name="A",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("x", models.IntegerField()),
+            ],
+        ),
+    ]